MIT OpenCourseWarehttp://ocw.mit.edu 6.033 Computer System EngineeringSpring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.M.I.T. DEPARTMENT OF EECS6.033 - Computer System Engineering Traceroute Hands-On AssignmentHands-on 3: Internet Routes and Measuring Round Trip TimesComplete the following hands-on assignment. Do the activities described, and hand in the answers to the numbered questions at the beginning of Recitation 11. Please hand in t yped responses, not hand-written.In this assignment you will get a chance to experiment with two very useful and widely-used network diagnostic tools, traceroute and ping, to expose youto some of the interesting quirks in network routing and packet round trip times.We recommend, but do not require, that you perform this assignment on Athena. Part of this assignment cannot be completed onathena.dialup.mit.edu due to security restrictions. Please note that the TAs cannot guarantee tech support if you do not use an Athena workstation. Ineither case, please make sure you use a workstation on the MIT network. Some results may be quite different if you use an off-campus network.0. Measuring Round Trip Times With PingIn the first two exercises, you will use the ping utility to send echo requests to a number of different hosts. The ping utility is one of the more useful utilitiesfor testing a network. It allows you to measure the time that it takes for a packet to travel through the Internet to a remote host and back. The ping utilityworks by sending a short message, called an echo-r eque st , to a host using the Internet Control Message Protocol (ICMP). A host that supports ICMP (andmost do) and receives an echo-request message simply replies by sending an echo-response back to the originating host.In many of the exercises, you will be referring to hosts via their DNS names rather than their IP addresses. (For more information about Internet hostnamesand DNS, and how these relate to IP addresses, please see Section 4.4 of the course notes.)For more information about ping, look at the man page on ping and the specifications for ICMP, located in RFC 792. Section 7.4.4 of the course notesdescribe ICMP as well.athena% man pingTo use the ping command on Athena, run a command such as:athena% ping www.google.comIf you run ping from a Sun workstation, you may have to use the -s option to get it to display the results that you want. Type machtype to determine thetype of machine you are using. If you have any more questions, see the man pages for more details on how to use ping.This course makes use of Athena, MIT's UNIX-based computing environment. OCW does not provide access to this environment.A. Round Trip Times:In the following two questions, you are asked to use the ping utility to measure the round trip times to several hosts on the Internet.For the following hosts, send 10 packets, each with a length of 56 data bytes. Note: You may find that the packet responses are 64 bytes instead of 56 bytes.Look at RFC 792 to find out the reason.The hosts are:www.csail.mit.edu www.berkeley.edu www.usyd.edu.auwww.kyoto-u.ac.jpQuestion 1: Indicate what percentage of packets sent resulted in a successful response. For the packets from which you received a response,write down the minimum, average, and maximum round trip times in milliseconds. Note that ping reports these times to you if you tell it howmany packets to send on the command line.Question 2: Explain the differences in minimum round trip time to each of these hosts.Question 3: Now send pings with 56, 512 and 1024 byte packets to the 4 hosts above. Write down the minimum, average, and maximum round trip times inmilliseconds for each of the 12 pings. Why are the minimum round-trip times to the same hosts different when using 56, 512, and 1024 byte packets?B. Unanswered Pings:For the following hosts, send 100 packets that have a length of 56 data bytes. Indicate what percentage of the packets resulted in a successful response.www.wits.ac.za (University of the Witwatersrand, Johannesburg)www.microsoft.com Question 4: For some of the hosts, you may not have received any responses for the packets you sent. What are some reasons as to why youmight have not gotten a response? (Be sure to check the hosts in a web browser.)1. Understanding Internet routes using tracerouteAs the name implies, traceroute essentially allows you to trace the entire route from your machine to a remote machine. The remote machine can bespecified either as a name or as an IP address.Theathena.dialup.mit.edu machines have security restrictions against using icmp sockets. Icmp has been disabled on the dialups because icmptraffic can be used to explore the topology of the network and a compromised athena account results in easy access to the powerful dialup machines. You'llneed to use an accessible linux machine or visit a cluster in order to complete the traceroute portion of the hands-on.We include a sample output of an execution of traceroute and explain the salient features. The command:% traceroute www.google.comtries to determine the path from the source machine (vinegar-pot.mit.edu) to www.google.com. The machine encountered on the path after the first hopis NW12-RTR-2-SIPB.MIT.EDU, the next is EXTERNAL-RTR-1-BACKBONE-2.MIT.EDU, and so on. In all, it takes 13 hops to reach py-in-f99.google.com.The man page for traceroute ( athena% man traceroute ) contains explanations for the remaining fields on each line.% traceroute www.google.comtraceroute: Warning: www.google.com has multiple addresses; using 64.233.167.99traceroute to www.l.google.com (64.233.167.99), 30 hops max, 40 byte packets 1 NW12-RTR-2-SIPB.MIT.EDU (18.181.0.1) 0.476 ms 0.318 ms 0.237 ms 2 EXTERNAL-RTR-1-BACKBONE-2.MIT.EDU (18.168.1.18) 0.827 ms 0.624 ms 0.753 ms 3 EXTERNAL-RTR-2-BACKBONE.MIT.EDU (18.168.0.27) 1.097 ms 0.772 ms 0.887 ms 4 207.210.142.233 (207.210.142.233) 0.578 ms 0.549 ms 0.713 ms 5 207.210.142.1 (207.210.142.1) 0.750 ms 2.530 ms 1.178 ms 6 207.210.142.2 (207.210.142.2) 5.886 ms 15.387 ms 5.762 ms 7 64.57.29.21 (64.57.29.21) 24.732 ms 24.693 ms 24.695 ms 8 72.14.236.215 (72.14.236.215) 31.733 ms 27.588 ms 216.239.49.34 (216.239.49.34) 27.810 ms 9 66.249.94.235 (66.249.94.235) 12.495 ms 209.85.252.166 (209.85.252.166) 36.961 ms 26.459 ms10 216.239.46.224 (216.239.46.224) 33.736 ms 33.396 ms 209.85.248.221 (209.85.248.221) 26.130 ms11 66.249.94.133
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